Nitriding



Patented May 16, 1933 UNITED STATES PATENT OFFICE- JOHN J. EGAN, OF BROOKLYN, NEW YORK, ASSIGNOR TO ELECTRO METALLURGICAL COMPANY, A CORPORATION OF WEST VIRGINIA N ITRIDING No Drawing.

My invention relates to the production of nitride cases on ferrous materials by heat ng the materials in the presence of nitriding agents, and it is the main objects of my invention to intensify or accelerate the production of such cases.

Thin, hard, wear-resistant cases on ferrous alloys are useful as wearing surfaces for machine parts. The cases may be produced by nitriding, i. e. by heating the alloys in the presence of nitriding agents to temperatures below the nitride eutectoid temperature. In a nitriding gas, such as ammonia, a treatment of 12 to 20 hours is required to produce the cases, the treating time usually being longer when lower temperatures are used than when. higher temperatures are used. The hard, wear-resistant cases are usually produced by heating in an atmosphere of ammonia to about 460 C.'to 580 0., the treated alloy containing a promot ng agent, such as aluminum or vanadium, WhlCh promotes the formation of the hard, wearresistant coating at these temperatures. By

' far the most extensive use of my invention is in connection with the production of hard,

Wear-resistant coatings and the invention will be described with reference thereto.

It has been found that the action of hitriding agents is intensified when certain carbon compounds containing oneor more N0 radicals are present.

As illustrative of my invention, a specimen of ferrous alloy containing about 95.5% iron, about 1% aluminum, and small amounts of phosphorus, sulphur, manganese, silicon, nickel, molybdenum and carbon was placed in a closed container. Ammonia was bubbled through nitrobenzene which was heated to a temperature just below its boiling point to increase its vapor pressure. The entrapped air in the container was. displaced by the mixture of ammonia and nitrobenzene vapor and the container and its contents were heated to 460 C. for 4 hours whilst a slow current of the gas mixture was passed into the container.- A thin, uniform, wear-resistant case having a hardness corresponding to about 1000 Brinell was produced on the specimen. A similar hard, wear-reslstant Application filed February 26,1930. Serial No. 431,640.

case was produced on another specimen of the samealloy when heated for 16 hours in ammonia. without the presence of nitrobenzcne Vapor. In the treatment with ammonia and without nitrobenzene, no appreciable hardness was produced by heating the alloy at 460 C. for 4 hours.

Acceleration may be produced by the use of higher molecular weight carbon chain compounds containing one or more N0 radicals, as for example niono-nitrotoluene. The accelerators of my invention are characterized by the symbol RM in which R represents one or more aliphatic or closed carbon chain radicals and M represents one or more- NO radicals linked to a carbon radical.

Any appreciable amount of the accelerator in co-njunctionwith the nitriding agent is sufiicient to produce acceleration. The pre ferred amount to be used with an alloy under given conditions may be determined by experiment for each particular case, but different amounts of the accelerator than those which produce the quickest results maybe used. Considerations of cost, make it desirable not to use excessive amounts of the accelerator substance.

Although I have given only a few specific examples of accelerators and only one example of a nitriding agent, it is evident that other substances of the classes described may be used and modifications of the described method may be made without departing from my invention. Therefore, I do not wish to be understood as imposing limitations on my invention except such as are imposed by the prior art and by the annexed claims.

I claim:

1. The method of producing nitride cases on ferrous materials which comprises heat ing the material at nitriding temperatures below the eutectoid atabout 600 C. in the presence of a nitriding agent and one. of the following substances: nitrobenzene, mononitrotoluene.

'2. The method of producing nitride cases on ferrous materials which comprises heating the material at nitriding temperatures below the eutectoid at about 600 C. in the presence of a nitriding gas and one of the following substances: nitrobenzene, mono-nitrotoluene.

3. The method of producing nitride cases on ferrous materials which comprises heat- 5 ing the material at nitriding temperatures below the eutectoid at about 600 C. in the presence of ammonia and at least one of the following substances: nitrobenzene, mononitrotoluene. 1 4. Method ofaccelerating the production of nitride cases on ferrous materials by heating the materials in the presence of ammonia which comprises effecting said nitriding in the presence of at least one accelerating agent 1 chosen from the group consisting of nitrobenzene and the mononitro-monoalkyl benzenes.

In testimony whereof, I afix my signature.

JOHN J. EGAN. 

